Astronomische Nachrichten Astronomical Notes RE PR INT Modeling a Maunder minimum

Keywords magnetohydrodynamics (MHD) –turbulence –Sun: activity –Sun: magnetic fields We introduce on/offintermittencyinto amean field dynamo model by imposing stochastic fluctuations in either the alpha effect or through theinclusion of afluctuatingelectromotivef orce. Sufficiently strong smallscalefluctuations with time scales of theorder of 0.3–3 years can produce long term variations in thesystem on timescales of theorder of hundreds of years.However,global suppression of magnetic activity in bothhemispheres at once wasnot observed. Thevariationofthe magnetic field does not resemblethat of thesunspot number,but is more reminiscent of the 10 Be record.The interpretation of our results focuses attentiononthe connectionbetween thelevel of magnetic activity and thesunspot number,anissue that must be elucidated if long term solar effectsare to be wellunderstood. Key words magnetohydrodynamics (MHD) – turbulence – Sun: activity – Sun: magnetic fields We introduce on/off intermittency into a mean field dynamo model by imposing stochastic fluctuations in either the alpha effect or through the inclusion of a fluctuating electromotive force. Sufficiently strong small scale fluctuations with time scales of the order of 0.3–3 years can produce long term variations in the system on time scales of the order of hundreds of years. However, global suppression of magnetic activity in both hemispheres at once was not observed. The variation of the magnetic field does not resemble that of the sunspot number, but is more reminiscent of the 10 Be record. The interpretation of our results focuses attention on the connection between the level of magnetic activity and the sunspot number, an issue that must be elucidated if long term solar effects are to be well understood.